Magnetic recording/reproducing apparatuses such as a video tape recorder using a magnetic tape as a medium have been put into practical use and become widely available. Further, various companies have achieved smaller apparatuses and developed digitization with higher density recording. In order to increase a recording density and obtain compatibility, it is important to accurately perform tracking on a head and a track. As a technique for accurately performing tracking, an ATF (Automatic Track Finding) control method has been known as a method replacing a conventional tracking control method using a fixed head and a control signal. The levels of pilot signals leaking from both sides of a track to be scanned by a head during reproduction are compared with each other by frequency-multiplexing or modulating a pilot signal into an information signal for recording, or performing recording in a bursting manner while dividing an area from an information signal, so that tracking control is performed (e.g., Japanese Unexamined Patent Publication No. 59-92460). This method has been already applied and put into practical use for an 8-millimeter VTR, a digital VTR, and so on.
FIGS. 10(a) and 10(b) are diagrams showing the operating principle of a conventional magnetic recording/reproducing apparatus.
In FIG. 10(b), reference numerals 1a and 1c denote heads opposed to each other by 180 degrees on a rotary cylinder 2, reference numeral 3 denotes a PG pulse detector for detecting a rotational phase of the rotary cylinder 2, and reference numeral 4 denotes an FG pulse detector for detecting a rotating speed of the rotary cylinder 2.
In FIG. 10(a), reference numeral denotes a magnetic tape, reference numerals 6a to 6c denote tracks for recording information signals, and reference numeral 6f denotes a starting track of consecutive recording. Reference numeral 7a denotes a capstan motor which is contact-bonded by a pinch roller 8 and performs feed control of the magnetic tape 5, reference numeral 7b denotes an FG pulse detector of the capstan motor 7a, reference numeral 9 denotes a head switching control section for switching the heads 1a and 1c in turn at proper timing, and reference numeral 32 denotes a capstan motor control section which controls a speed of the capstan motor 7a according to an output pulse of the FG pulse detector 7b and performs phase control according to an output of an ATF control unit 15 using a pilot signal included in a reproduction signal of the head 1a. 
First, referring to FIG. 10(a), an operation for reproducing a recorded tape will be discussed.
When the head 1a scans the track 6b, in addition to an information signal recorded on the track 6b, pilot signals f1 and f2 leak into the head 1a from the adjacent tracks 6a and 6c. After the pilot signals f1 and f2 included in a reproduction signal of the head 1a are extracted and rectified by band-pass filters 12a and 12b and rectifiers 13a and 13b, a difference between the signals is outputted as a tracking error signal by a difference unit 14, and a capstan control circuit 23 performs phase control according to the error signal. In this way, the capstan motor control section 32 performs control so that the center line of the head 1a always scans the center line of a desired track (the track 6b in this example).
Next, a head switch generating operation will be discussed.
As shown in FIG. 10, a head switch generating circuit (hereinafter, referred to as an HSW generating circuit) 10 selects the head for scanning a track by switching a head switch 11 according to pulses PG and FG detected by PG pulse detector 3 and the FG pulse detector 4.
FIG. 11 shows the detailed configuration of the HSW generating circuit 10, and FIG. 12 shows a process of forming a head switching pulse HSW.
The HSW generating circuit 10 is constituted by D flip-flops 33 and 34 and a NOT circuit 35. In this case, an example is illustrated in which PG is outputted one time for one rotation of the rotary cylinder 2 and FG of four periods is outputted. In this example where the two heads are opposed to each other by 180 degrees on the rotary cylinder 2, a head switching pulse HSW is reset at the timing of PG and is formed so that the H/L level is inverted every two periods of FG.
Further, when a recording starting point on a track is determined only by the output of a rotational position sensor of the rotary cylinder 2, erasing occurs partially on an area not to be erased on a previously recorded adjacent track in the case of consecutive recording and inserting edition between magnetic recording/reproducing apparatuses which are different in recording position on a tape due to mechanical variance, an adjustment error, and so on. In order to solve this problem, as shown in FIG. 13, a method is available in which a positioning signal is recorded on a first area of a track and an information signal is recorded on a second area (e.g., Japanese Unexamined Patent Publication No. 8-263940).
Moreover, consecutive recording and inserting edition are performed from a track 6f (FIG. 10) in response to an instruction for starting recording after a proper time tape is reproduced until an editing point and a pre-roll operation is performed for matching a track width and the like on the editing point.
In this way, various companies have achieved smaller magnetic recording/reproducing apparatuses using magnetic tape as a media such as a video tape recorder and developed digitization. Thus, it is necessary to reduce the number of heads mounted on a rotary cylinder in order to achieve a smaller rotary cylinder and reduce the cost. A method has been devised for usually performing all of reproduction, pre-roll reproduction for consecutive recording and edition, and recording by using a head with a width larger than a track width, and a method has been devised for performing recording and reproduction of formats having different track widths by using the head.
In this case, the following problem arises during pre-roll reproduction of consecutive recording and edition: as shown in FIG. 14, since the center line of the head 1a scans the center line of the track 6b under ATF control, when recording is performed in this state, a part originally recorded on the previous track 6a is erased by a width of (Wh−Wt)/2 (diagonally shaded part 6e) in the case of head width Wh>track width Wt.
Therefore, as a result of consecutive recording, the last track width of originally recorded substrate tracks is (3·Wt−Wh)/2, resulting in a thinned track as compared with the other tracks each having a width of Wt. Namely, when consecutive recording is performed by a head having a head width larger than a track width under ATF control, track thinning occurs on a joining point and thus lowers the reproduction level of the track, thereby affecting picture quality and sound quality.
The present invention relates to such a conventional problem and has as its object the provision of a magnetic recording/reproducing apparatus which does not cause track thinning on a joining point even when consecutive recording is performed by a head wider than a track width.